This proposal describes a five-year plan for Brian Wainger to achieve independence as an investigator who uses patient-derived motor neurons to study amyotrophic lateral sclerosis (ALS). The candidate is a neurologist at Massachusetts General Hospital. He has a strong research background in electrophysiology and molecular biology, as well as recent successful experience recording from patient-derived motor neurons, a technique that he will apply to the proposed project. Dr. Clifford Woolf, the primary mentor, is Professor of Neurology and Neurobiology at Harvard Medical School and Director of the Neurobiology Program at Children's Hospital Boston. He is a world expert in neuroscience, and has supervised numerous trainees who now hold academic faculty positions. Dr. Kevin Eggan, the co- mentor, is an HHMI Early Career Scientist and Professor in the Department of Stem Cell and Regenerative Biology and the Harvard Stem Cell Institute. He is a leader in the stem cell field and in ALS research. An advisory committee of senior scientists able to provide additional expert guidance includes also Dr. Merit Cudkowicz and Dr. Bruce Bean. The research will be performed at Children's Hospital. ALS is a devastating, untreatable neurological disease characterized by progressive weakness and death of neurons in the motor system. Most cases are sporadic, but about 10% are familial. The primary function of a motor neuron is to collect and integrate signals from the brain and spinal cord and transmit an outgoing electrical signal that results in muscle contraction. The researchers hypothesize that investigating the electrical properties of healthy and diseased motor neurons will help increase understanding of ALS and yield insight into how to treat the disease. Using recent advances in stem-cell technology, the investigators have derived motor neurons from ALS and control subjects and found that motor neurons derived from patients with familial ALS are hyperexcitable, meaning that they are prone to too much activity, and that the hyperexcitability may contribute to motor neuron death in ALS. The proposed project consists of evaluating hyperexcitability and motor neuron death in a range of inherited and sporadic variants of ALS. The project will yield a mechanistic understanding and characterization of the observed hypexcitability, specifically with regard to the role of voltage-gated potassium ion channels. Through the training program, the investigator will acquire critical expertise using techniques in stem cell biology and single cell RNA expression analysis, as well as didactic exposure to key components of translational medicine such as biostatistics and trial design. With these skills, the applicant will successfully complete the proposed project and transition to independence, where he can exploit this novel approach of modeling human neurological disease using human neurons more broadly.